So I'm restoring an Eico HF12A 6BQ5-output mono tube amplifier that's in great shape physically. I've found that one of the plate circuit windings in the power transformer (160V? I can't remember off hand) is shorted and giving only 15VAC. Likely this is why it was retired I'm assuming. All the other windings are spot on for expected voltage. What are the chances I could track down a replacement power transformer? Is this something that might be rewindable? I'm at a brick wall and hate to have to scrap this one. What kind of options do I have realistically?

Eico has been out of business close to 40 years now; the chances of finding a NOS or OEM transformer are pretty slim unless you take it out of a junker amp. It will probably be necessary to come up with a generic substitute. Rewinding the original transformer is a possibility, but paying a shop to do it may not be cost effective.

The schematic shows two secondaries, a 6.3-volt heater winding and a HV winding. The voltage chart on page 8 indicates that the HV winding was 280-0-280 volts (560 volts centertapped). The tube line-up is three 12AX7's wired for parallel heater operation, 0.9 amps; two EL84's at 0.76 amps heater current each for 1.52 amps; and one EZ81 with a 1.0 amp heater. Total is 3.42 amps heater load, so the 6.3 volt winding needs to be rated for at least 3.5 amps or more. Primary is 120 volts, of course. Note that the HV winding voltage may be allowed to vary a little bit; if you found a transformer with, say, a 550-volt or 575-volt centertapped winding it would still work fine.

Bigger problem is going to be matching up the size and bolt pattern of the original transformer, so you don't have to cut or drill any chassis metal. (This is not usually a good idea due to the metal filings, vibration, and other physical violence to the unit, and it also greatly reduces any future collector value since it cannot be reversed). I would take the transformer off the chassis and carefully measure the opening size, the bolt hole locations, and the height of the transformer above the chassis, and go from there.

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Joined: May Sat 06, 2006 4:03 amPosts: 2876Location: ZIP 23831 South of Richmond, VA 25 miles down the pike.

I pulled the SAMS thinking there might be some suggested replacements for the power transformer but none. The SAMS data for transformer and other voltages vary a bit. Is the part number on your power transformer 30019? Mfr and date code? Wonder what the "A" means?

You may be in luck! Heyboer Transformers, Grand Haven MI, was the OEM for Eico equipment, AND they are still in business AND they will do special orders for replacement power and audio transformers. I had a new power trans. built for a HF-81, exact fit and has a 120volt primary vs. the 110 volt original.

Hmmm. I may still have one of these HF12 power transformers (I robbed the OPT off of a rusted-out derelict HF12 to fix a Stromberg-Carlson ASR333 stereo amp a long time ago, and kept the PT, I think). Time to go digging a bit...

Regards,Gordon.

_________________"It's the guys who think that attending meetings is real day's work that are the problem."- HepcatWilly (on AudioKarma)

Hi. Did you measure the secondary resistance? I have had transformers open up and give low voltage output like this and was able to follow the wires into the transformer and re solder the winding to the lead and fixed the problem. Corrosion can set up in the joint. If it were shorted turns the other windings would also be low output due to the load being inductively coupled. This would cause the transformer to run hot and burn up so I bet your trouble may be repairable if you can get at the bad connection.